Photovoltaic module start-up for the International Space Station

The International Space Station (ISS) US on-orbit segment electric power system (EPS) uses four photovoltaic modules (PVMs). Each PVM consists of solar array wings (SAW) for converting solar flux to electric power, nickel-hydrogen batteries for electric energy storage, electronic boxes for electric voltage control and power switching, and a thermal control system for maintaining selected PVM components within their normal operating temperature ranges. The start-up consists of deploying the SAW and photovoltaic radiator, initialization and check out of all hardware, thermally conditioning batteries and charging batteries. After start-up, each PVM power channel is able to generate, store and distribute electric power to ISS loads. Electric power to support start-up of the first PVM is provided via two auxiliary power converter units (APCUs), one per channel. During sunlit periods, the SAW provides power for the battery heaters (for thermal conditioning, as needed) and battery charging. During eclipse periods, the APCU maintains the channel in a standby mode. After start-up is complete, the APCU is disconnected and the PVM operates independently. The process used to start-up the first PVM on the ISS is described in this paper. Procedures used to bring dormant batteries to their normal operating temperature range and then to charge them to 100% state of charge are also described